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Technical Bulletin 2/14

THE SNMP PROTOCOL

The SIMPLE NETWORK MANAGEMENT

PROTOCOL, SNMP is a widely used

management protocol that operates on top of

IP and UDP protocols. In the basic mode of

operation the SNMP is a Request / Response

protocol. The requesting, controlling process is

called the Manager and the process

responsible for providing the responses is

called the Agent. In the SATELLAR use case,

the SATELLAR modem will act as a SNMP

Agent and the monitoring PC or SCADA would

be the SNMP Manager.

THE SNMP REQUEST

SNMP requests can be either Get or Set type.

The Get request queries for a value of the

parameter from the managed device and the

Set writes a new value for the parameter.

The requested parameters are identified with

OID (Object Identifier). For example, the value

for the device temperature would be identified

by the OID: 1.3.6.1.4.1.30306.1.1.1.4.2.1.1.0 .

MIB

Mappings between OID numbers and

parameters are stored in a tree formatted

hierarchical database called Management

Information Base, MIB. To enable SNMP query

of a certain parameter, both the Manager and

the Agent must have respective OID available

in their MIB. For SATELLAR-2DS/20DS modem,

the MIB database contents for SATELLAR related

parameters are available for download at

SATEL web pages. After download, they can be

installed or imported to the Manager MIB.

SIMPLE NETWORK MANAGEMENT PROTOCOL

SATELLAR MANAGEMENT WITH SNMP GET AND SET

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The following drawing illustrates the SNMP Get

operation in more detail. The SCADA system has

been configured to periodically monitor the

temperature of the SATELLAR modems in the

network. The SCADA system has a MIB entry

stored for the SATELLAR specific parameter, so the

SCADA will be able to map the temperature

parameter to the correct OID. This OID is then

included in the request. When the request is

received by the SATELLAR, it will map the OID to

the requested parameter of temperature. The

internal logic in the SATELLAR reads the

temperature value and sends it in the SNMP

response back to SCADA. Again, in the response

the identifier for the requested parameter is the

OID. The monitored SATELLAR device can be

either locally connected or remote modem behind

the IP radio interface. The SATELLAR network must

be configured to operate in the Packet Mode.

However, if it is sufficient to monitor only locally

connected modem, radio protocol mode can be

selected freely.

SCADA SUPPORT

Many SCADA solutions have a built-in support

for the SNMP. Also, many SCADA providers

recommend SNMP usage by adding a protocol

gateway to the system. The protocol gateway

will convert the SCADA supported protocol to

SNMP queries and vice versa. For example ABB

Microscada supports the SNMP operation via

the SNMP-OPC (Open Connectivity via Open

Standards) gateway. See the following drawing

for the illustration for the gateway operation.

45°C

The OPC gateway

mediates and

translates the OPC-

SNMP communication.

In this case, the MIB

resides at the OPC

Gateway, instead of

SCADA.

SCADA

SATELLAR Packet Mode

(IP operation) required.

For local monitoring,

the radio protocol

mode can be selected

Monitored device

can be any SNMP

enabled device with

Agent functionality.

SNMP GET OPERATION

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The following drawing illustrates the SNMP Set

operation in more detail. The user wants to enable

the Serial IP functionality of the remote SATELLAR

by setting the Serial IP to Server mode. The

management PC has the MIB configured and thus

it is able to map the correct parameter to the OID,

together with the desired value. In the following

example, this is the step 1.): Serial IP mode is

identified by the OID

1.3.6.1.4.1.30306.1.1.1.4.2.1.1.15 and the

“Server mode” is represented by the value 1. The

manager sends this information to the SNMP

Agent running in the remote SATELLAR, and issues

the parameter value change with SNMP SET

request, as illustrated in the step 2.). In the step

3.), the SNMP Agent receives the Set request and

again, maps the OID to the correct parameter,

together with the received value 1. In this

example, MIB query was successful, as well as

setting the parameter in the step 4.). Therefore,

the SNMP Agent at the remote SATELLAR replies to

the Manager by sending the SNMP SET Response,

together with the status indication (no errors), the

changed OID, and the value. Remote

configuration with SNMP Set protocol was

successful.

SNMP TIMEOUT

When the SNMP Get or Set Request has been

sent by the Manager application, the Manager

expects the Response to arrive within a specified

time, SNMP Timeout. If there is no response

received, the SNMP Manager application stops

the communication with the agent. Therefore,

in SATELLAR networks with radio links, it is

recommended to increase the timeout value set

in the Manager. How this is done, depends on

the application.

SNMP SET OPERATION

1. SNMP GET Request

2. Timeout

3. Retry: SNMP Get

4. Delayed response

5. No response:

operaon halted.

SNMP PARAMETERS IN THE SATELLAR

Services

SNMPD State:

Turns the SNMP functionality on or off.

SNMP

SNMP RO Community:

Password to query values from this device with

SNMP Get commands. The Manager side

configuration must be set to match with this

string.

SNMP RW Community:

Password to set values to this device with SNMP

Set commands. The Manager side configuration

must be set to match with this string.

SNMP RW Community IP:

IP address range that is allowed to send Set

commands to this device.

SNMP Notification IP:

The IP address of the destination that his device

sends the SNMP notifications to, when such a

notification is available.

ENABLING SNMP OPERATION

First step to enable SNMP operation in

SATELLAR is to download the MIB files from the

SATEL web pages, from Support, Downloads,

Firmware section (April 7, 2014:

http://www.satel.com/support/downloads/

firmware). Import all the MIB files to the

Manager application. The details on how this is

done fully depend on the selected manager

application. Files needed are:

Next, configure the SNMP parameters with a

web browser connection to SATELLAR IP–

address. Required parameters are in Modem

Settings tab, on the Services page as well as

on the SNMP configuration page.

FEW SNMP MONITORING SOFTWARE EXAMPLES

LAN State Pro

 Commercial monitoring tool

 Designed for large IP networks

 Restricted set of SNMP functionality

 Controllable set: no extra messaging

 Visual monitoring available

 Viewing normal values requires mouse over

 Working and extensive alarm functionality

 Free 30-day trial

SATEL does not currently provide any SNMP

Manager applications. One reason for this is that

many systems already have an operational SNMP

Manager. However, if the 3rd party SNMP

manager is required, several options can be

found from the Internet. Available software varies

a lot. Many of them are complex and heavy

solutions with full of features and functionality that

would not be needed in the SATELLAR network

management. This makes the usage of the

application clumsy and slow. Some applications

also often lack of the visual presentation of the

network and the

monitoring state. Another issue with many

applications is that they are sending extensive

amount of SNMP Get queries for values that one

might not be interested about. And in many cases

there is no way to suppress these messages or

control which SNMP requests to send and how

often.

According to the SATEL testing of SNMP

Managers, currently the most interesting ones

seem to be applications called “LAN State Pro”

and “The Dude.”

The Dude

 Free and open monitoring tool

 Extensive set of SNMP functionality

 Some functionalities generate additional

messaging and cannot be turned off

 Configurable and extensive visual

monitoring

 Working and extensive alarm functionality

 Scripting functionality

3RD PARTY MANAGER APPLICATIONS